Collision tumour of actinic keratosis and basal cell carcinoma with different dermoscopic features

Background: Collision tumours are rare neoplastic lesions consisting of different benign and malignant tumours in the same anatomical site. Various intrinsic and extrinsic factors such as ageing, skin type, UV exposure may lead development of different tumoural lesions. Objective: The aim of the present study was to identify and clarify dermoscopic features of collision tumour of actinic keratosis and basal cell carcinoma which can be a diagnostic pitfall both clinically and dermoscopically. Methods: Dermoscopic features of five histopathologically-proven collision tumours of actinic keratosis and basal cell carcinoma and their dermatopathological correlates were retrospectively analysed. Results: On dermoscopy, coiled vessels surrounded by a whitish halo were detected in one lesion. Small blue-gray blotches were detected in all lesions even located on periphery or centrally. White circles, prominent follicular openings, four dot structures (rosettes) were detected in one lesion. Pink structureless areas were detected in three of the lesions. Conclusion: Clinicians should consider collision tumour when a lesion contains dermoscopic features of more than one type of tumour.